In recent years, with the advances made in the miniaturization of electronic devices, integration densities of IC (SSI, MSI, LSI and VLSI) chips have been greatly increased. In mounting of semiconductor elements onto a substrate, the distance (pitch) between electrodes has been reduced while the number of input/output(I/O) terminals has been increased. In card type calculators and IC cards, a demand has arisen for developing low-profile products which require short pitches.
Wireless bonding, such as TAB and flip chip, can advantageously realize collective bonding of electrodes and high-precision alignment between electrodes. As a result, low-profile and automatic mounting of semiconductor elements with high reliability can be expected. Therefore, wireless bonding has become a mainstream mounting technique for LSI chips.
In performing wireless bonding, metal projections known simply as bumps are generally formed on aluminum electrodes of LSI chips. The present methods and apparatus for creating these bumps suffer from several drawbacks. Obtaining a bump height which is substantially greater than the bump width is difficult to obtain. Bump-to-bump positional accuracy is hard to maintain. Bumps are expensive to create with the cost of extremely small bumps (e.g. 0.5 mils or smaller) being quite expensive.